We report the complete 5025-base sequence of the human 28S rRNA gene. Variability within the species has been demonstrated by sequencing a variable region from six separately cloned genes. This region is one of three large subunit rRNA regions that show extreme sequence and size variation among species. The interspecies differences suggest species-specific functions for these sections, while the intraspecies heterogeneity indicates differences among ribosomes.Comparison of the human gene with a partial sequence from the chimpanzee 28S gene yields divergence rates for the two species: 0.8% for conserved regions of the gene and 3.7% for a variable region. The rapid divergence rates of variable regions in the ribosomal gene may permit answers to the question of time of separation of closely related species.

A series of clones of human natural killer (NK) cells was characterized with respect to expression of the Ti alpha and Ti beta genes of the T-cell receptor. T11+T3+ NK clones contained Ti alpha and Ti beta RNA transcripts and expressed disulfide-linked heterodimers, demonstrating the presence of a functional T-cell receptor. In contrast, T11+T3- NK clones expressed only 1.0-kilobase truncated Ti beta transcripts, without a Ti alpha transcript and no detectable surface Ti protein. Since previous studies demonstrated that Ti beta gene activation precedes Ti alpha gene activation in thymic ontogeny, the T11+T3- NK cells appear to be derived from T-lineage precursors.

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The acute effects of mineralo- and glucocorticoids on urinary electrolyte excretion were studied in the conscious, acutely potassium deprived, adrenalectomized rat. Sodium, potassium, and creatinine were measured in the urine excreted from 2.5 to 5.5 h after injection of one or more of the following steroids: aldosterone (Aldo), 9-alpha fluorocortisol (FC), deoxycorticosterone (DOC), dexamethasone (Dex), and spironolactone (Spiro). The hierarchy (a) for increasing creatinine excretion was Dex greater than FC greater than Aldo greater than DOC greater than Spiro greater than none, a hierarchy consistent with glucocorticoid potency; and (b) for producing anti-natriuresis was Aldo greater than DOC greater than or equal to FC greater than or equal to none = Spiro greater than Dex, a hierarchy consistent with mineralocorticoid potency. In contrast, the kaliuresis produced by mineralo- and glucocorticoids appears different. A "mineralocorticoid" kaliuresis is 1) elicited by anti-natriuretic doses of Aldo and FC, 2) approximately twice control UKV, 3) unrelated to changes in glomerular filtration rate (GFR), and 4) inhibited by Spiro. A "glucocorticoid" kaliuresis is 1) elicited by Dex and high doses of Aldo and FC, 2) about seven to twenty-fold greater than control UKV, 3) possibly dependent, in part, on changes in GFR, and, 4) not inhibited by Spiro. DOC was not kaliuretic at anti-natriuretic doses. The urinary Na/K ratio was an unreliable index of mineralocorticoid action.

T cell receptors for antigen and major histocompatibility complex (MHC) ~ determinants have, using anticlonotypic monoclonal antibodies (mAb), been defined on inducer, suppressor, and class I and class II MHC-specific cytotoxic T lymphocytes as T3oassociated molecules of 90 kilodaltons (kD) molecular mass (1-8). These cionotypic structures, termed Ti, are comprised of one 49-54 kD a and one 43 kD/3 subunit, which are disulfide linked. Peptide mapping analysis of isolated Ti a and/3 subunits from clones of differing specificities demonstrated that clonally unique peptides as well as shared peptides existed in each subunit, thus implying that variable (V) as well as constant (C) domains existed within Ti and/3 molecules (5, 9). Subsequently, N-terminal amino acid sequencing and molecular cloning techniques led to identification of the Ti /3 gene structure, and showed that specific V-, D-(diversity), J-(joining), and C-like segments fuse to form an active/3 gene (10-16). These studies also indicated that the N-terminal V domains were encoded by nucleotides derived from V, D, and J segments. Similar characterization of Ti o~ subunits suggests that each contains a unique NH2 V domain created by joining dispersed germline genes (17-21). In addition to the similarities between joining processes of T cell receptor and Ig gene segments, both structures manifest distant but clearcut homology at protein and DNA levels.T cell receptors, like B cell receptors, must accommodate a myriad of different antigenic specificities in order to provide the organism with an efficient system for immunologic recognition. Moreover, since T cells generally recognize antigen in the context of polymorphic MHC determinants, it is reasonable to assume that V region structural diversity of the T cell population will be no less complex than that of B lymphocytes. In the case of B cells, five mechanisms account for Abbreviations used in this paper: C, constant region of Ig; cDNA, complementary DNA; CML, ceil-mediated lympholysis; Con A, concanavalin A; D, diversity-generating segment of Ig; FITC, fluorescein isothiocyanate; IEF, isoelectric focusing; IL-2, interleukin 2;J,joining region of Ig; mAb, monoclonal antibody; MHC, major histocompatibility complex; mRNA, messenger RNA; PAGE, polyacrylamide gel electrophoresis; PHA, phytohemagglutinin; SDS, sodium dodecyl sulfate; TdR, thymidine deoxyribose; Ti, T cell receptor; V, variable region of Ig. 1326J. ExP. MED.

To further characterize sequential events involved in activation of genes encoding the T-cell receptor (a complex of T3 molecules and a disulfide-linked heterodimer designated Ti, T3-Ti) for antigen and the major histocompatibility complex during intrathymic ontogeny, cDNA probes specific for Ti a and Ti 13 subunits were used for transcriptional analysis. Ti The human T-cell receptor is a molecular complex consisting of the monomorphic 20-and 25-kDa T3 molecules and a noncovalently associated clonotypic 90-kDa disulfide-linked heterodimer termed Ti (1-3). Whereas the T3 molecules are likely involved in specialized signal transduction, the Ti subunit presumably serves as the binding site for nominal antigen and major histocompatibility complex (MHC) gene product ligands (4,5). The 43-kDa p subunit of a given Ti molecule is encoded by variable (V)-, diversity (D)-, joining (J)-, and constant (Cl-like elements that rearrange during ontogeny to form an active Ti gene (6-13). Likewise, a similar set of germ-line segments fuse to generate an active Ti a gene (10,(14)(15)(16)(17)(18). The diversity of V domains in the Ti a and Ti p subunits that give rise to a myriad of receptor specificities are created by combinatorial, junctional, and chain-associationmediated diversity analogous to parallel mechanisms that account for diversity within immunoglobulin molecules (10,11,(19)(20)(21)(22).Assembly and expression of Ti molecules unique to the T-cell lineage occurs within the specific inductive microenvironment of the thymus (3, 23). The nature by which this process evolves is of considerable interest, especially in view of the fact that immunocompetent function first appears within this circumscribed microenvironment prior to peripheral exportation in association with ongoing T3-Ti receptor selection events, which delete high-affinity autoreactive T-cell receptor structures (24). To obtain information about the ontogeny of the T-cell antigen/MHC receptor, a Ti ,B-subunit cDNA probe and heteroantisera specific for the Ti a and p subunit were utilized to characterize T-lineage cells (23). Analysis of thymic tumors and normal thymocytes at both the DNA and protein levels demonstrated that Ti p gene rearrangements occurred early in intrathymic ontogeny. In contrast, surface expression of Ti a and Ti , molecules was exclusively restricted to the mature thymocyte population.The relatively early appearance of Ti P-subunit gene rearrangement and late expression of surface T-cell receptors suggested that one of the other components of the T3-Ti complex might be activated later in ontogeny. To explore this possibility, we herein analyzed Ti a and Ti-, transcripts from thymocytes and clonal T-lineage tumor populations corresponding to one or another stage of intrathymic ontogeny. MATERIALS AND METHODSLymphoid Cell Populations. Portions of human thymus (age 2 months to 2 years) were taken at the time of corrective cardiac surgery and used as the source of thymocytes (25). Immune rosettes were formed by the method of Griffin...

Recent studies using cloned antigen-specific T lymphocytes and monoclonal antibodies directed at their various surface glycoprotein components have led to the identification of the human T-cell antigen receptor as a surface complex comprised of a clonotypic 90-kD Ti heterodimer and the invariant 20- and 25-kD T3 molecules. Approximately 30,000-40,000 Ti and T3 molecules exist on the surface of human T lymphocytes. These glycoproteins are acquired and expressed during late thymic ontogeny, thus providing the structural basis for immunologic competence. The alpha and beta subunits of Ti bear no precursor-product relationship to one another and are encoded by separate genes. Moreover, the presence of unique peptides following proteolysis of different Ti molecules isolated by non-cross-reactive anticlonotypic monoclonal antibodies supports the notion that variable regions exist within both the alpha and the beta subunits. N-Terminal amino acid sequencing and molecular cloning of the Ti beta subunit further show that it bears an homology to the first V-region framework of immunoglobulin light chains and represents the product of a gene that rearranges specifically in T lymphocytes. Triggering of the T3-Ti receptor complex gives rise to specific antigen-induced proliferation through an autocrine pathway involving endogenous IL-2 production, release, and subsequent binding to IL-2 receptors. The implications of these findings for understanding human T-cell growth and its regulation in disease states are discussed.

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